The invention concerns frozen aerated products, a method for manufacturing same, and a device for implementing the method.
Conventional methods for manufacturing frozen aerated products, in particular ice cream, comprise operations for mixing, homogenizing, pasteurizing, freezing, and hardening the mixture to be frozen. Aeration of the mixture or expansion is carried out at the freezing stage in a proportion such that the volume increases by 70 to 120%. On leaving the freezing device (freezer), the temperature of the aerated mass is typically xe2x88x925 to xe2x88x926xc2x0 C. The aerated mass is then hardened at xe2x88x9240 to xe2x88x9245xc2x0 C. in a hardening chamber, until the core temperature of the product reaches xe2x88x9218 xc2x0 C. or less for bulk products or xe2x88x9230xc2x0 C. for extruded products in bars.
Attempts have been made to lower the temperature of the mass on leaving the freezer, to save energy and with the aim of improving its texture, for example in the sense of greater smoothness. With conventional equipment, however, problems of high viscosity of the mass of ice cream at temperatures below xe2x88x927 to xe2x88x928xc2x0 C. have been an insurmountable problem. This problem has been resolved, in part, by using two scraped surface freezers in series. The first freezer is a conventional freezer and delivers aerated ice cream at a temperature of about xe2x88x927xc2x0 C. and the second is specially designed to process the highly viscous mass so as to lower its temperature to around xe2x88x9210xc2x0 C.
Similarly, EP-A- 0561 118 describes a three-stage method for producing ice cream at low temperature, down to around xe2x88x9220xc2x0 C. This is an output temperature at which the hardening stage can be completely eliminated for bulk products and appreciably shortened for extruded products. In the first, so-called pre-expansion, stage, air is incorporated into the mixture to be frozen at a positive temperature. In the second stage the aerated mass is cooled in a scraped surface exchanger, emerging at around xe2x88x926xc2x0 C. During the third stage a screw device cools the mass to around xe2x88x9220xc2x0 C.
U.S. Pat. No. 5,024,066 concerns a two-stage system. In the first stage a pre-expansion takes place during which air is added to the mass to be frozen at a positive temperature. In the second stage the aerated mass is cooled, by means of an Archimedes screw with a roughened surface fitted with scraper blades on its periphery, to a sufficiently low negative temperature to ensure that the frozen mass has a stable texture, allowing the products to be stored directly in cold storage.
There remains, however, a need for a method to manufacture frozen aerated products wherein the steps of expansion and cooling the frozen mass can be accomplished in a single device and in a single step.
The invention is directed to frozen aerated products. In one embodiment the frozen aerated product is fat free and has a mean ice crystal diameter of between about 20 to 60 microns and a mean equivalent diameter for the ice crystals of between about 32 and 36 microns. The frozen aerated product, without fat, may have an overrun between about 20 and 150 percent. The frozen aerated product, without fat, may have protein substantially homogeneously distributed through out the frozen aerated product. The protein may be casein.
In another embodiment the frozen aerated product contains fat and has a mean ice crystal diameter of between about 20 to 60 microns, a mean equivalent diameter for the ice crystals of between about 32 and 36 microns, and fat globules with a mean diameter of from about 8 to 20 microns. The overrun may be between about 20 and 150 percent. The fat may be substantially homogeneously distributed through out the frozen aerated product and the protein may be substantially homogeneously distributed through out the frozen aerated product. The protein may be casein.
The invention is also directed to a method for manufacturing a frozen aerated product. The method involves mixing, aerating, freezing, and cooling a liquid based composition to a temperature of less than or equal to xe2x88x928 xc2x0 C. in a single stage followed by extruding the composition to provide a frozen aerated product having a mean ice crystal diameter of between about 20 to 60 microns and a mean equivalent diameter for the ice crystals of between about 32 and 36. The liquid based composition may be introduced into the stage at about 2 to 5xc2x0 C. The liquid based composition may be mixed, aerated, frozen, and cooled in a casing that contains two parallel endless co-rotating screws, turning in the same direction while meshing with each other. The co-rotating screws may turn at about 100-600 r/min and the liquid based composition may be aerated to about 20-150% overrun and cooled to about xe2x88x928 to xe2x88x9220xc2x0 C. before being extruded.